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Introduction
Weeds are the most harmful pest among those targeted by pesticides for arable crops but they are also are beneficial (e.g. feeding wild fauna). If herbicides are the most effective to control them, their consequences on health and environment compel to reduce their use. To achieve this goal, farmers need to combine several partially effective techniques. While the effects of each technique are known, it is much more difficult (if not impossible) to predict short-term and long-term effects of their combination. During the COPRAA project, we demonstrated in different farmer groups that providing them with specific knowledge inputs and model results, is an effective way of motivating them and helping them in the design process, as it enables them to take both time scales into account.
Material and methods
Three workshops were held in each group of farmers, over a period of a few months: presentation of our method and definition of weed issues for at least one farmer; design of an innovative cropping system by the other members; discussion about the results of our assessment. The performances of each cropping system for weed management were assessed with the virtual field FLORSYS (Colbach et al., 2021), a mechanistic model simulating crop and weeds development and competition for light and nitrogen. DEXiPM (Pelzer et al., 2012) was used to assess the sustainability of the designed cropping systems.
Evaluation results for co-designed systems
The assessment of several innovative cropping systems with FLORSYS has pointed out three main trends (see one example in Table 1):
1. Although weed harmfulness for crop production increased a little in most of innovative systems, it remained low.
2. These performances are achieved while reducing significantly or even stopping herbicide use.
3. Mixed effects are observed on weed contribution to biodiversity: increase in food offer for wild fauna, but a decrease in weed species richness and/or evenness.
Results of discussions with farmers
Reducing or stopping the use of herbicides without increasing weed harmfulness implies multiple and significant changes in the cropping system, which may have consequences for its sustainability. We have submitted to the farmers the results of the multicriteria assessment (economic, social and environmental sustainability) performed with DEXIPM. These results have raised discussion on important subjects for farmers, such as the effect of tillage (especially ploughing) on soil fertility, the need to purchase new machinery, the technical know-how and outlets for new crops... The workshops with the farmer groups were also an opportunity to discuss about their perception of weed infestation in their fields and its long-term impact for the cropping system management. In our example, these discussions led to modifications of the succession of crops in the innovative system (column “Innovative system (2nd version)” in Table 1).
Conclusion
Mechanistic models, such as FLORSYS, are useful to answer questions of farmers or advisors when they design cropping systems in order to solve weed management issues. However, such models are complex to use, require a lot of input data and the length of simulations is not compatible with the duration of a workshop with farmers. That is why a simpler tool, DECIFLORSYS based on meta-modelisation, has been designed and completed during the project. Il will allow advisors to compute results for a cropping systems assessment in a few minutes.
Moreover, we carried out similar approaches in other groups with different production contexts and group composition (with or without advisors). The diversity of situations will make it possible to create a guide for the design of innovative systems aimed at sustainable weed management, specifying how the models can be used in the process.
Table 1: Performances of the current and innovative systems of a farmer in terms of weed management. There is no use of herbicides in the innovative systems (organic farming). Indicators are an average over total length of simulation (30 years) and are normalized: 1 is the best performance (green), 0 the worst one (red).
References
Colbach et al., 2021. The FLORSYS crop-weed canopy model, a tool to investigate and promote agroecological weed management. Field Crops Res. 261, 108006. https://doi.org/10.1016/j.fcr.2020.108006
Pelzer et al., 2012. Assessing innovative cropping systems with DEXiPM, a qualitative multi-criteria assessment tool derived from DEXi. Ecological Indicators, 18, 171-182. Doi: 10.1016/j.ecolind.2011.11.019
| Keywords | weed management; model; cropping system design; combination of practices |
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